U.S. patent application number 10/914042 was filed with the patent office on 2005-03-24 for organic electroluminescent device, method for manufacturing the same, and electronic appliance.
Invention is credited to Takei, Shuichi.
Application Number | 20050064239 10/914042 |
Document ID | / |
Family ID | 34317213 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050064239 |
Kind Code |
A1 |
Takei, Shuichi |
March 24, 2005 |
Organic electroluminescent device, method for manufacturing the
same, and electronic appliance
Abstract
An organic EL device includes a cathode, organic luminescent
layers, and an electron-injection layer disposed between the
cathode and the luminescent layers. The electron-injection layer
contains an organic metal complex having a central atom of the same
metal element as a constituent element of the cathode. A larger
number of ligands than the valence of the central atom of the
complex are coordinated to the central atom.
Inventors: |
Takei, Shuichi;
(Nagano--ken, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
34317213 |
Appl. No.: |
10/914042 |
Filed: |
August 6, 2004 |
Current U.S.
Class: |
428/690 ; 257/89;
313/504; 313/506; 427/66; 428/917 |
Current CPC
Class: |
H01L 51/5092 20130101;
H01L 51/0077 20130101; Y10S 428/917 20130101; H01L 27/3211
20130101; H01L 51/0037 20130101 |
Class at
Publication: |
428/690 ;
428/917; 313/504; 313/506; 257/089; 427/066 |
International
Class: |
H05B 033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2003 |
JP |
2003-290644 |
Aug 8, 2003 |
JP |
2003-290645 |
Jun 21, 2004 |
JP |
2004-182526 |
Claims
What is claimed is:
1. An organic electroluminescent device comprising: an anode; a
cathode; an organic luminescent layer disposed between the anode
and the cathode; and an electron-injection layer disposed between
the cathode and the organic luminescent layer, comprising an
organic metal complex comprising a central atom of the same metal
element as at least one constituent element of the cathode.
2. The organic electroluminescent device according to claim 1, the
organic metal complex comprising a larger number of ligands than
the valence of the central atom.
3. The organic electroluminescent device according to claim 1, the
organic luminescent layer comprising plural types of organic
luminescent layer segments having different luminescent colors; the
electron-injection layer comprising plural types of
electron-injection layer segments corresponding to the individual
types of organic luminescent elements; the organic metal complex
being selected for each type of organic luminescent layer segments;
and each type of electron-injection layer segments comprising the
organic metal complex selected for the corresponding type of
organic luminescent layer segments.
4. The organic electroluminescent device according to claim 1, the
organic luminescent layer comprising plural types of organic
luminescent layer segments having different luminescent colors; the
organic metal complex being selected for each type of organic
luminescent layer segments; and the electron-injection layer
comprising the organic metal complexes.
5. The organic electroluminescent device according to claim 2, the
ligands of the organic metal complex comprising a chelating ligand
and a neutral ligand.
6. The organic electroluminescent device according to claim 1, the
central atom of the organic metal complex comprising an alkali
metal, an alkaline earth metal, magnesium, or a rare earth
metal.
7. The organic electroluminescent device according to claim 1, the
organic metal complex being a .beta.-diketone complex.
8. The organic electroluminescent device according to claim 1, the
organic luminescent layer comprising a polymeric material.
9. A method for manufacturing an organic electroluminescent device,
comprising the steps of forming an organic luminescent layer;
forming an electron-injection layer; and forming a cathode, wherein
the step of forming an electron-injection layer comprises a substep
of depositing a first organic metal complex comprising the same
number of chelating ligands as the valence of an central atom
thereof with an organic material for a neutral ligand to form a
second organic metal complex comprising a larger number of ligands
than the valence of the central atom thereof.
10. The method for manufacturing an organic electroluminescent
device according to claim 9, wherein, at the step of forming an
organic luminescent layer, plural types of organic luminescent
layer segments having different luminescent colors are formed; and,
at the step of forming an electron-injection layer, the first
organic metal complex being selected for each of organic
luminescent layer segments, and the first organic metal complexes
being deposited with the organic material for a neutral ligand.
11. A method for manufacturing an organic electroluminescent
device, comprising the steps of forming an organic luminescent
layer; forming an electron-injection layer; and forming a cathode,
wherein the step of forming an electron-injection layer comprises
the substeps of: forming a first organic metal complex film by
applying a coating solution containing a first organic metal
complex comprising the same number of chelating ligands as the
valence of an central atom thereof; and forming a film of a second
organic metal complex comprising a larger number of ligands than
the valence of the central atom thereof on the organic luminescent
layer by depositing an organic material for a neutral ligand on the
first organic metal complex film.
12. The method for manufacturing an organic electroluminescent
device according to claim 11, wherein, at the step of forming an
organic luminescent layer, plural types of organic luminescent
layer segments having different luminescent colors are formed; and,
at the substep of forming a first organic metal complex film, the
first organic metal complex is selected for each of organic
luminescent layer segments, and a coating solution containing the
first organic metal complexes is applied onto the organic
luminescent layer segments.
13. The method for manufacturing an organic electroluminescent
device according to claim 11, wherein, at the step of forming an
organic luminescent layer, plural types of organic luminescent
layer segments having different luminescent colors are formed; and,
at the substep of forming a first organic metal complex film, the
first organic metal complex is selected for each of organic
luminescent layer segments, and each of coating solutions
containing the different first organic metal complexes is applied
onto the corresponding type of organic luminescent layer segments
by droplet discharging.
14. The method for manufacturing an organic electroluminescent
device according to claim 9, the central atom of the organic metal
complex comprising the same metal element as at least one
constituent element of the cathode.
15. An electronic appliance comprising the organic
electroluminescent device according to claim 1.
Description
RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application Nos. 2003-290644 filed Aug. 8, 2003; 2003-290645 filed
Aug. 8, 2003, and 2004-182526 filed Jun. 21, 2004 which are hereby
expressly incorporated by reference herein in their entirety.
BACKGROUND
[0002] The present invention relates to an organic
electroluminescent device, a method for manufacturing the device,
and an electronic appliance including the device.
[0003] An electron-injection layer plays an important role in
organic electroluminescent devices (hereinafter referred to as
organic EL devices). The luminescent characteristics of organic EL
devices greatly depend on the structure of the electron-injection
layer. Conventionally, the electron-injection layer is composed of
an inorganic material such as lithium fluoride (LiF) and calcium
(Ca). Although LiF and Ca are originally insulators, a thin film of
LiF or Ca provides an electron-injection effect.
[0004] The above materials, however, cannot provide excellent
characteristics for all of red (R), green (G), and blue (B)
luminescent layers. For example, LiF can provide an excellent
electron-injection effect only for B luminescent layers.
[0005] To solve the problem, for example, Japanese Unexamined
Patent Application Publication No. 2000-243569 proposes an organic
EL device including an electron-injection layer composed of an
organic metal complex. This complex has a central atom of an alkali
metal and a chelating ligand coordinated to the central atom. If
such a complex is disposed between an organic luminescent layer and
an inorganic cathode, the complex provides high adhesion at both
interfaces to enhance the luminescent characteristics of all of R,
G, and B luminescent layers. In addition, for example, the above
structure can be applied to top-emission organic EL devices to
enable a brighter display because a transparent cathode including a
metal complex can be readily formed.
[0006] The above device, however, cannot provide sufficient
luminescent efficiency, and therefore still higher luminescent
efficiency is expected. In this device, additionally, the central
atom of the complex may be separated from the ligand to diffuse
into the luminescent layer as an impurity during the formation of
the cathode, thus failing to provide stable characteristics.
[0007] An object of the present invention, which aims at solving
the above problems, is to provide an organic EL device that can
provide an excellent electron-injection effect for all of R, G, and
B luminescent layers and that has stable luminescent
characteristics, a method for manufacturing the device, and an
electronic appliance including the device.
SUMMARY
[0008] To achieve the above object, the present invention provides
an organic EL device including an anode; a cathode; an organic
luminescent layer disposed between the anode and the cathode; and
an electron-injection layer disposed between the cathode and the
organic luminescent layer. The organic luminescent layer is
composed of, for example, a polymeric material. The
electron-injection layer contains an organic metal complex having a
central atom of the same metal element as at least one constituent
element of the cathode. In the present invention, the term
"electron-injection layer" also means "electron-transport layer,"
which has an electron-transport property, and "hole-blocking
layer," which blocks holes to keep them in the luminescent
layer.
[0009] According to the present invention, the organic metal
complex is used for the electron-injection layer to enhance the
adhesion of the electron-injection layer to the cathode, which is
composed of a metal, and to the luminescent layer, which is
composed of an organic material. This electron-injection layer can
therefore improve the luminescent efficiency of each type of red
(R), green (G), and blue (B) luminescent layers. According to the
present invention, particularly, the above complex has a central
atom of the same metal element as a constituent element of the
cathode. Such a complex can further increase the adhesion between
the electron-injection layer and the cathode, thus providing still
higher electron-injection efficiency. Furthermore, the central atom
of the complex is of the same metal element as at least one
constituent element of the cathode. The complex can therefore
reliably hold the cathode material to inhibit the diffusion of the
cathode material into the luminescent layer, thus providing stable
luminescent characteristics.
[0010] The central atom of the above complex only needs to be of
the same metal element as a constituent element of the cathode in
the vicinity of the interface to the electron-injection layer (that
is, a constituent element of the cathode adjacent to the
electron-injection layer). When, for example, the cathode is
composed of a laminate of thin films, the central atom of the
complex only needs to be of the same element as a constituent
element of the thin film adjacent to the electron-injection
layer.
[0011] The cathode preferably contains a metal element having a low
work function (for example, an alkali metal, an alkaline earth
metal, magnesium, or a rare earth metal) to enhance
electron-injection efficiency. This metal element only needs to
exist at the interface to the electron-injection layer. If, for
example, the cathode is composed of a laminate of thin films, at
least the thin film adjacent to the luminescent layer is composed
of the above metal element having a low work function. If the
central atom of the complex is of the same metal element having a
low work function (for example, an alkali metal, an alkaline earth
metal, magnesium, or a rare earth metal), the complex can improve
the adhesion between the cathode and the electron-injection layer
and reduce the injection barrier for electrons, further enhancing
the luminescent efficiency. To achieve the above object,
preferably, the organic metal complex in the organic EL device of
the present invention has a larger number of ligands than the
valence of the central atom.
[0012] The known organic metal complex described above has a
central atom to which chelating ligands are coordinated. The number
of the ligands corresponds to the valence of the central atom. If
the central atom is of an element having a smaller valence number
(for example, an alkali metal), fewer ligands surround the central
atom (for example, the above known complex has one ligand).
Consequently, as described above, the central atom may be separated
from the ligands, depending on the deposition conditions of the
cathode. In general, the coordination number of the central atom is
larger than the valence of the central atom. If ligands other than
the chelating ligands (for example, neutral ligands such as
heterocyclic amines) are coordinated to the central atom as in the
present invention, the central atom can have a larger number of
ligands than the valence of the central atom. The coordination bond
of ligands other than the chelating ligands to the central atom can
increase the chemical stability of the complex. In addition, these
ligands surround the central atom to act as steric hindrance,
thereby stably holding the central atom. The present invention can
therefore increase the stability of the complex to inhibit the
intrusion of impurities into the luminescent layer, thus providing
an organic EL device having high luminescent efficiency and stable
characteristics. Furthermore, higher complex stability leads to
higher moisture resistance.
[0013] In the present invention, additionally, plural types of
organic luminescent layer segments having different luminescent
colors (for example, R, G, and B luminescent layer segments) may be
arrayed on a substrate to provide a full-color display. The
different types of luminescent layer segments, however, may have
different optimum complexes. In this case, preferably, the organic
metal complex is selected for each type of organic luminescent
layer segments, and the electron-injection layer contains the
organic metal complexes. The electron-injection layer, containing
all of the optimum organic metal complexes for the individual types
of luminescent layer segments, can have an excellent
electron-injection effect on all types of luminescent elements. In
addition, color balance can be adjusted by changing the mixing
ratio of the complexes.
[0014] Alternatively, preferably, the electron-injection layer is
composed of plural types of electron-injection layer segments
corresponding to the individual types of organic luminescent layer
segments; and each type of electron-injection layer segments
contains the organic metal complex selected for the corresponding
type of organic luminescent layer segments. In this case, the
organic metal complex for the electron-injection layer can be
selected for each type of organic luminescent layer segments, thus
enhancing the electron-injection property for each type of organic
luminescent layer segments and facilitating the adjustment of, for
example, the color balance of each type of luminescent layer
segments.
[0015] Various complexes including chelate complexes and crown
ether complexes, which are cyclic polyethers, may be used as the
above organic metal complex. Among them, a .beta.-diketone ligand
can form a stable metal complex (.beta.-diketone complex) because
the ligand acts as an acidic reagent and is a multidentate ligand
having oxygen atoms.
[0016] The present invention further provides a method for
manufacturing an organic EL device. This method includes the steps
of forming an organic luminescent layer; forming an
electron-injection layer; and forming a cathode. The step of
forming an electron-injection layer includes a substep of
depositing a first organic metal complex having the same number of
chelating ligands as the valence of an central atom thereof with an
organic material for a neutral ligand to form a second organic
metal complex having a larger number of ligands than the valence of
the central atom thereof.
[0017] This method can provide an organic EL device having high
efficiency and stable luminescent characteristics as described
above. According to this method, additionally, the formation of the
complex by co-deposition enables cathode design (including the
electron-injection layer) suited to the luminescent material used
because known complex and ligand materials can be freely combined
in a deposition machine. Furthermore, an organic metal complex
having any composition can be provided by changing deposition
conditions, so that the element structure can be readily
optimized.
[0018] At the step of forming an organic luminescent layer, plural
types of organic luminescent layer segments having different
luminescent colors (for example, R, G, and B luminescent layer
segments) may be arrayed on a substrate to provide a full-color
display. The different types of luminescent layer segments,
however, may have different optimum complexes. In this case,
preferably, at the step of forming an electron-injection layer, the
first organic metal complex is selected for each type of organic
luminescent layer segments, and the first organic metal complexes
are deposited with the organic material for a neutral ligand. The
electron-injection layer, containing all of the optimum organic
metal complexes for the individual types of luminescent layer
segments, can have an excellent electron-injection effect on all
types of luminescent elements. In addition, the color balance can
be adjusted by changing the mixing ratio of the complexes.
[0019] The present invention provides another method for
manufacturing an organic EL device. This method includes the steps
of forming an organic luminescent layer; forming an
electron-injection layer; and forming a cathode. The step of
forming an electron-injection layer includes the substeps of
forming a first organic metal complex film by applying a coating
solution containing a first organic metal complex having the same
number of chelating ligands as the valence of an central atom
thereof; and forming a film of a second organic metal complex
having a larger number of ligands than the valence of the central
atom thereof on the organic luminescent layer by depositing an
organic material for a neutral ligand on the first organic metal
complex film. This method is the same as the previous manufacturing
method except that a wet process (namely, coating) is employed;
therefore, this method can provide the same effect as the previous
method.
[0020] Also, in this method, at the step of forming an organic
luminescent layer, plural types of organic luminescent layer
segments having different luminescent colors (for example, R, G,
and B luminescent layer segments) may be arrayed on a substrate to
produce an organic EL device that can provide a full-color display.
In this case, preferably, at the substep of forming a first organic
metal complex film, the first organic metal complex is selected for
each type of organic luminescent layer segments, and a coating
solution prepared by mixing the first organic metal complexes in a
solvent (that is, a coating solution containing the first organic
metal complexes) is applied onto the organic luminescent layer
segments by, for example, spin coating to form an optimum
electron-injection layer for the individual types of luminescent
layer segments. The electron-injection layer, containing all of the
optimum organic metal complexes for the individual types of
luminescent layer segments, can have an excellent
electron-injection effect on all types of luminescent elements. In
addition, the color balance can be adjusted by changing the mixing
ratio of the complexes.
[0021] Alternatively, preferably, at the substep of forming a first
organic metal complex film, the first organic metal complex is
selected for each type of organic luminescent layer segments and is
used to prepare a coating solution for each type of organic
luminescent layer segments, and each of the coating solutions (that
is, coating solutions containing the different first organic metal
complexes) is applied onto the corresponding type of organic
luminescent layer segments by droplet discharging. Using droplet
discharging, in contrast to spin coating, each coating solution can
be selectively applied onto the corresponding type of organic
luminescent layer segments. This method therefore enables optimum
material design for each type of organic luminescent layer
segments. In addition, this method facilitates the adjustment of
color balance for each type of organic luminescent layer
segments.
[0022] In the above methods, preferably, the central atom of the
organic metal complex is of the same metal element as at least one
constituent element of the cathode. The electron-injection layer
and the cathode, containing the same element, can adhere more
strongly to each other, thus providing still higher
electron-injection effect. Furthermore, this element, even if
diffusing downward during the formation of the cathode, does not
act as an impurity on the electron-injection layer, thus providing
luminescent elements having stable electrical characteristics. The
central atom of the above complex only needs to be of the same
metal element as a constituent element of the cathode in the
vicinity of the interface to the electron-injection layer. When,
for example, the cathode is composed of a laminate of thin films,
the central atom of the complex only needs to be of the same
element as a constituent element of the thin film adjacent to the
electron-injection layer.
[0023] The present invention further provides an electronic
appliance including the above organic EL device. This electronic
appliance has a long life and can provide a bright display.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic wiring diagram of an organic EL device
according to an embodiment of the present invention.
[0025] FIG. 2 is a schematic plan view of the organic EL
device.
[0026] FIG. 3 is a sectional view taken along line A-B in FIG.
2.
[0027] FIG. 4 is a sectional view taken along line C-D in FIG.
2.
[0028] FIG. 5 is an enlarged sectional view of an essential part in
FIG. 3.
[0029] FIGS. 6A-B show sectional views illustrating steps of a
method for manufacturing the organic EL device.
[0030] FIGS. 7E-G show sectional views illustrating steps following
the steps in FIG. 6.
[0031] FIGS. 8H-J show sectional views illustrating steps following
the steps in FIG. 7.
[0032] FIGS. 9K-M show sectional views illustrating steps following
the steps in FIG. 8.
[0033] FIGS. 10N-O show sectional views illustrating steps
following the steps in FIG. 9.
[0034] FIG. 11 is a perspective view of an example of electronic
appliances according to the present invention.
DETAILED DESCRIPTION
[0035] An organic EL device according to an embodiment of the
present invention will now be described with reference to the
drawings.
[0036] Organic EL Device
[0037] FIG. 1 is a schematic wiring diagram of the organic EL
device according to this embodiment.
[0038] In FIG. 1, an organic EL device 1 is an active-matrix
display including thin-film transistors (hereinafter referred to as
TFTs) as switching elements.
[0039] This organic EL device 1 includes scanning lines 101, signal
lines 102 extending in a direction orthogonal to the scanning lines
101, and power lines 103 extending in parallel with the individual
signal lines 102. A pixel area X is provided in the vicinity of
each intersection point of the scanning lines 101 and the signal
lines 102.
[0040] The signal lines 102 are connected to a data-line drive
circuit 100 including a shift register, a level shifter, a video
line, and an analog switch. On the other hand, the scanning lines
101 are connected to a scanning-line drive circuit 80 including a
shift register and a level shifter.
[0041] Each pixel area X includes a switching TFT 112 having a gate
electrode that is supplied with a scanning signal via the scanning
lines 101; a hold capacitor 113 for holding a pixel signal supplied
from the signal lines 102 via the switching TFT 112; a drive TFT
123 having a gate electrode that is supplied with the pixel signal
held by the hold capacitor 113; a pixel electrode (anode) 23 into
which drive current flows from the power lines 103 when the pixel
electrode 23 is electrically connected to the power lines 103 via
the drive TFT 123; and a functional layer 110 held between the
pixel electrode 23 and a cathode 50. The pixel electrode 23, the
cathode 50, and the functional layer 110 constitute a luminescent
element (organic EL element).
[0042] In this organic EL device 1, when the scanning lines 101 are
driven to turn on the switching TFT 112, the potential of the
signal lines 102 at the time is held by the hold capacitor 113. The
state of the hold capacitor 113 determines whether the drive TFT
123 is on/off. Current flows from the power lines 103 into the
cathode 50 via the channel of the drive TFT 123, the pixel
electrode 23, and the functional layer 110. The functional layer
110 then emits light according to the amount of current flowing
through it.
[0043] The organic EL device 1 in this embodiment will now be
described in detail with reference to FIGS. 2 to 5.
[0044] First, the planar structure of the organic EL device 1 is
described with reference to FIG. 2.
[0045] The organic EL device 1 includes an electrically insulating
substrate 20; a pixel electrode region (not shown in the drawing)
in which the pixel electrodes connected to the switching TFTs (not
shown in the drawing) are arranged in a matrix on the substrate 20;
a power line (not shown in the drawing) disposed around the pixel
electrode region and connected to the individual pixel electrodes
23; and a pixel part 3 (outlined by the one-dot chain line in FIG.
2) that is substantially rectangular in plan view and is positioned
at least above the pixel electrode region. In the present
invention, the substrate 20 and components formed thereon,
including the switching TFTs, various circuits, and interlayer
insulating films, as will be described later, are collectively
referred to as a base part.
[0046] The pixel part 3 is divided into a central effective display
region 4 (outlined by the two-dot chain line in FIG. 2) and a dummy
region 5 (the region between the one-dot chain line and the two-dot
chain line in FIG. 2) disposed around the effective display region
4.
[0047] In the effective display region 4, display areas R, G, and B
each of which includes the pixel electrode 23 are arranged in a
matrix at intervals in the A-B and C-D directions.
[0048] The scanning-line drive circuit 80 is disposed on each of
the left and right sides of the effective display region 4 in FIG.
2. These scanning-line drive circuits 80 are disposed below the
dummy region 5.
[0049] A check circuit 90 is disposed on the top side of the
effective display region 4 in FIG. 2. This check circuit 90 checks
the operational state of the organic EL device 1. For example, the
check circuit 90 includes a check information output device (not
shown in the drawing) for externally outputting check results to
check the quality of displays and inspect them for defects during
manufacture and before shipment. The check circuit 90 is disposed
below the dummy region 5.
[0050] A drive voltage is applied from a predetermined power source
to the scanning-line drive circuits 80 and the check circuit 90 via
drive voltage conducting parts 310 (see FIG. 3) and 340 (see FIG.
4). In addition, a drive control signal is transmitted and a drive
voltage is applied from, for example, a predetermined main driver
for controlling the operation of the organic EL device 1 to the
scanning-line drive circuits 80 and the check circuit 90 via drive
control signal conducting parts 320 (see FIG. 3) and a drive
voltage conducting part 350 (see FIG. 4). The drive control signal
is a command signal transmitted by, for example, the main driver to
control the signal output of the scanning-line drive circuits 80
and the check circuit 90.
[0051] The sectional structure of the organic EL device 1 is then
described with reference to FIGS. 3 to 5. FIG. 3 is a sectional
view taken along line A-B in FIG. 2. FIG. 4 is a sectional view
taken along line C-D in FIG. 2. FIG. 5 is an enlarged view of an
essential part in FIG. 3.
[0052] In FIGS. 3 and 4, the organic EL device 1 is sealed by
attaching a sealing substrate 30 to the substrate 20 with a sealing
resin 40.
[0053] If the organic EL device 1 has a bottom-emission structure,
the substrate 20 is composed of a transparent or translucent
material so that the organic EL device 1 can emit light through the
substrate 20. Examples of the material used include glass, quartz,
and resins (plastic materials and films). In particular, an
inexpensive soda glass substrate is preferably used as the
substrate 20.
[0054] If, on the other hand, the organic EL device 1 has a
top-emission structure, the substrate 20 may be composed of either
a transparent or nontransparent material because the organic EL
device 1 emits light through the sealing substrate 30, that is, the
opposite side of the substrate 20. Examples of the nontransparent
material used include ceramics such as alumina, sheets that are
composed of a metal such as stainless steel and are subjected to an
insulation process such as surface oxidation, thermosetting resins,
and thermoplastic resins.
[0055] The sealing substrate 30 may be composed of, for example, an
electrically insulating board. For the top-emission structure, the
sealing substrate 30 is composed of a transparent material such as
glass, quartz, and a resin. The sealing resin 40 is composed of,
for example, a thermosetting resin or an ultraviolet curable resin,
preferably an epoxy resin, which is a thermosetting resin.
[0056] A circuit part 11 including various components such as the
drive TFTs 123 for driving the pixel electrodes 23 is formed on the
substrate 20, and the luminescent elements are provided on the
circuit part 11. As shown in FIG. 5, these luminescent elements are
formed by stacking the pixel electrodes 23, the functional layers
110, and the cathode 50 in that order. The functional layers 110
mainly include a luminescent layer 60.
[0057] The pixel electrodes 23 serve as anodes for supplying holes
to the luminescent layers 60. For the bottom-emission structure,
for example, the pixel electrodes 23 are composed of a transparent
conductive material such as indium tin oxide (ITO) and an amorphous
transparent conductive film based on indium oxide and zinc oxide
(indium zinc oxide (IZO.RTM.); manufactured by Idemitsu Kosan Co.,
Ltd.). For the top-emission structure, on the other hand, the
material for the pixel electrodes 23 is not limited to such a
transparent conductive material, and may be, for example, a
reflective or nontransparent conductive material such as aluminum
(Al) and silver (Ag).
[0058] The luminescent layer 60 may be composed of a known
fluorescent or phosphorescent material. Preferred examples of the
luminescent material used include polyfluorenes (PF),
poly(p-phenylene vinylene)s (PPV), polyphenylenes (PP),
poly(p-phenylene)s (PPP), polyvinylcarbazole (PVK), polythiophenes,
poly(dialkylfluorene) (PDAF), poly(fluorene-benzothiadiaz- ole)
(PFBT), poly(alkylthiophene) (PAT), and polysilanes such as
poly(methylphenylsilane) (PMPS).
[0059] The polymeric material to be used may be doped with another
polymeric material such as a perylene dye, a coumarin dye, and a
rhodamine dye; or a low-molecular-weight material such as rubrene,
perylene, 9,10-diphenylanthracene, tetraphenylbutadiene, Nile red,
coumarin 6, and quinacridone.
[0060] The term "polymer" herein refers to polymers having a higher
molecular weight than "low-molecular-weight materials," which have
a molecular weight on the order of a few hundred. The above
polymeric materials include not only macromolecules, which have a
molecular weight not less than 10,000, but also oligomers, which
have a molecular weight not more than 10,000.
[0061] In this embodiment, a set of the luminescent layers 60,
which correspond to red (R), green (G), and blue (B), are arrayed
in each pixel to provide a full-color display.
[0062] In this embodiment, hole-injection/transport layers 70 (see
FIG. 5) may be optionally provided between the pixel electrodes 23
and the luminescent layers 60. These hole-injection/transport
layers 70 block electrons traveling through the luminescent layers
60 efficiently, thus increasing the possibility of recombination
between electrons and holes in the luminescent layers 60. The
hole-injection/transport layers 70 are preferably composed of a
material having a low injection barrier for holes from the pixel
electrodes 23 to provide high hole mobility. Examples of such a
material include polythiophenes and polypyrroles, which may be
doped. A specific example of the material used is a dispersion of
poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate)
(PEDOT/PSS). This dispersion is prepared by dispersing
poly(3,4-ethylenedioxythiophene) in poly(styrene sulfonate), as a
dispersion medium, and further dispersing it in water.
[0063] In FIGS. 3 to 5, the cathode 50 has a larger area than the
total area of the effective display region 4 and the dummy region
5, and covers the effective display region 4 and the dummy region
5. For the top-emission structure, for example, the cathode 50 is
composed of a transparent conductive material. A preferred example
of such a material is a co-deposited film of bathocuproine (BCP)
and cesium (Cs). More preferably, ITO is deposited on the
co-deposited film of BCP and Cs to increase the conductivity.
Alternatively, an ultrathin Ca film (having a thickness of, for
example, about 5 nm) may be formed instead of the co-deposited film
of BCP and Cs, and ITO may be deposited on the ultrathin Ca film.
For the bottom-emission structure, on the other hand, the material
for the cathode 50 is not limited to such a transparent conductive
material, and may be a reflective or nontransparent conductive
material such as Al.
[0064] The cathode 50 preferably contains a metal element having a
low work function (for example, an alkali metal, an alkaline earth
metal, magnesium, or a rare earth metal other than promethium) to
enhance electron-injection efficiency. This metal element only
needs to exist at the interface of the cathode 50 on the side of
the luminescent layers 60. If, for example, the cathode 50 is
composed of a laminate of thin films, at least the thin film
adjacent to the luminescent layers 60 is composed of the above
metal element having a low work function. Specifically, a cathode
having high electron-injection efficiency can be provided by
forming a Ca film having a thickness of about 20 nm and then
forming an Al film having a thickness of about 200 nm on the Ca
film. The Al film also functions as a reflective layer for
reflecting light to the substrate 20.
[0065] In this embodiment, an electron-injection layer 52
containing an organic metal complex is provided between the cathode
50 and the luminescent layers 60 to enhance the efficiency of the
electron injection from the cathode 50 into the luminescent layers
60. This complex is an organic metal compound represented by the
general formula MAnBm, where M is a central atom of a metal
element; A is an organic chelating ligand; B is an organic neutral
ligand; n is the valence of the central atom M; and m is zero or a
natural number. Various complexes including chelate complexes and
crown ether complexes may be used as the complex for use in this
embodiment.
[0066] Preferred examples of the chelating ligand A include
.beta.-diketone ligands such as acetylacetone (acac),
dipivaloylmethane (dpm), hexafluoroacetylacetone (hfa),
2,2,6,6-tetramethyl-3,5-octanedione (TMOD), thenoyltrifluoroacetone
(TTA), and 1-phenyl-3-isoheptyl-1,3-propa- nedione (trade names:
LIX 54 and LIX 51; Henkel Corp.); quinolinol ligands such as
8-quinolinol (oxine) and 2-methyl-8-quinolinol; phosphate ligands
such as trioctylphosphine oxide (TOPO), tributyl phosphate (TBP),
isobutyl methyl ketone (MBK), and bis(2-ethylhexyl) phosphate
(D2EHPA); carboxylate ligands such as acetic acid and benzoic acid;
and diphenylthiocarbazone. Among them, a .beta.-diketone ligand can
form a stable complex (.beta.-diketone complex) because the ligand
acts as an acidic reagent and is a multidentate ligand having
oxygen atoms.
[0067] On the other hand, preferred examples of the above neutral
ligand B include pyridine (py) and heterocyclic amines such as
2,2'-bipyridine (bpy), 1,10-phenanthroline (phen),
2,9-dimethyl-1,10-phenanthroline (dmp), bathophenanthroline
(b-phen), and bathocuproine (bcp).
[0068] In this electron-injection layer 52, the central atom M may
be of the same metal element as a constituent element of the
cathode 50 to improve the adhesion between the electron-injection
layer 52 and the cathode 50. In this case, the central atom M only
needs to be of the same metal element as a constituent element of
the cathode 50 in the vicinity of the interface to the
electron-injection layer 52. When, for example, the cathode 50 is
composed of a laminate of thin films, the central atom M only needs
to be of the same metal element as a constituent element of the
thin film adjacent to the electron-injection layer 52.
Specifically, if the cathode 50 is composed of an Al monolayer
film, the complex used is, for example, Al(acac).sub.2 .bpy, which
has a central atom of the same metal element as a constituent
element of the cathode 50. If, additionally, the cathode 50 is
composed of a laminate of Ca and Al films, the complex used is, for
example, Ca(acac).sub.2 .bpy. The central atom M of this complex is
Ca, which exists on the side of the electron-injection layer 52 in
the cathode 50. If, furthermore, the cathode 50 is composed of a
co-deposited film of BCP and Cs, the complex used is, for example,
Cs(acac).sub.2 .bpy. The complex used may contain no neutral ligand
B, that is, may be an organic metal compound represented by the
general formula MA.sub.n, where M, A, and n are defined above.
[0069] According to this embodiment, not only the chelating ligand
A but also another ligand, namely the neutral ligand B, are
intentionally coordinated to the central atom M to increase the
chemical stability of the complex. In addition, the chelating
ligand A and the neutral ligand B surround the central atom M to
act as steric hindrance, thereby stably holding the central atom M.
This embodiment can therefore increase the stability of the complex
to inhibit the intrusion of impurities into the luminescent layers
60, thus providing an organic EL device having high luminescent
efficiency and stable characteristics.
[0070] If the cathode 50 is composed of a metal element having a
low work function, the central atom M of the complex is of a metal
element such as an alkali metal, an alkaline earth metal,
magnesium, and a rare earth metal. Such a complex has a high
electron affinity and a low injection barrier for electrons,
further enhancing the luminescent efficiency.
[0071] In this embodiment, furthermore, complexes suited to the
individual types of the luminescent layers 60 may be contained in
the electron-injection layer 52. When, as in this embodiment, each
pixel includes R, G, and B luminescent layers, the different types
of luminescent layers may have different optimum complexes. For
example, a complex having a central atom of strontium (Sr) exhibits
a large electron-injection effect on R luminescent layers, but a
small effect on B luminescent layers. On the other hand, for
example, a complex having a central atom of Li exhibits a large
effect on B luminescent layers, but an insufficient effect on R and
G luminescent layers. If, therefore, organic metal complexes suited
to the individual types of the luminescent layers 60 are contained
in the electron-injection layer 52, these complexes can
functionally complement each other to further enhance the
luminescent efficiency.
[0072] Alternatively, optimum metal complexes selected for the
individual types of the luminescent layers 60 may be selectively
provided on the corresponding types of the luminescent layers 60.
In other words, the electron-injection layer 52 may be separately
provided on each luminescent layer 60 so that each
electron-injection layer 52 can contain only the metal complex
selected for the corresponding type of the luminescent layers 60.
This design enables the use of an optimum material and easy
adjustment of color balance for each type of the luminescent layers
60.
[0073] The above complex may be used alone or in combination with a
known material having an electron-transport property. Examples of
such a known electron-transport material include cyclopentadienes,
oxadiazoles, bisstyrylbenzenes, p-phenylene compounds,
phenanthrolines, and triazoles. The electron-injection layer 52
preferably has a thickness of 0.1 to 1 nm to ensure the
conductivity.
[0074] The present invention is particularly preferably applied to
organic EL devices including a polymer luminescent layer. An
organic EL device including a polymer luminescent layer and a
cathode or electron-injection layer composed of an inorganic
material such as Ca has difficulty in the adhesion between the
luminescent layer and the cathode. In particular, polymeric
materials, which have a molecular weight of about 1,000 to 300,000,
have a significantly different molecular structure from those of
low-molecular-weight materials. Consequently, for example, the
polymer luminescent layer and the inorganic cathode have
significantly different thermal expansion coefficients, which may
cause the deterioration of the luminescent element at a high
temperature. An electron-injection layer composed of an organic
metal complex can function as a buffer layer to adhere firmly to
the cathode and the luminescent layer. In addition, the electrical
properties of such an electron-injection layer are intermediate
between those of the polymeric material for the luminescent layer
and the inorganic material for the cathode. Thus this
electron-injection layer also functions as an electrical buffer
layer to promote the injection of electrons into the luminescent
layer. Accordingly, it is preferred to deposit an organic
luminescent layer composed of a polymeric material having a
molecular weight of about 1,000 to 300,000, an electron-injection
layer composed of an organic metal complex having a molecular
weight of about 100, and an inorganic cathode in that order.
[0075] The structure of the circuit part 11 for driving the
luminescent elements is described with reference to FIG. 5.
[0076] In FIG. 5, the circuit part 11 is provided below the
luminescent elements. This circuit part 11 is formed on the
substrate 20 to constitute the base part. An underlying protective
layer 281 mainly composed of SiO.sub.2 is formed on the substrate
20, and a silicon layer 241 is formed on the underlying protective
layer 281. A gate insulating layer 282 mainly composed of SiO.sub.2
or SiN is formed on the silicon layer 241.
[0077] The silicon layer 241 has a channel region 241a overlapping
with a gate electrode 242 with the gate insulating layer 282
disposed therebetween. The gate electrode 242 is a part of the
scanning lines 101, which are not shown in FIG. 5. A first
interlayer insulating layer 283 mainly composed of SiO.sub.2 is
formed on the gate insulating layer 282, which covers the silicon
layer 241 and on which the gate electrode 242 is formed.
[0078] The silicon layer 241 further has a lightly doped source
region 241b and a heavily doped source region 241S on the source
side of the channel region 241a, and has a lightly doped drain
region 241c and a heavily doped drain region 241D on the drain side
of the channel region 241a; that is, the silicon layer 241 has a
lightly doped drain (LDD) structure. The heavily doped source
region 241S is connected to a source electrode 243 via a contact
hole 243a extending through the gate insulating layer 282 and the
first interlayer insulating layer 283. The source electrode 243 is
a part of the power lines 103 described above (extending from the
source electrode 243 in the direction perpendicular to the paper in
FIG. 5; see also FIG. 1). On the other hand, the heavily doped
drain region 241D is connected to a drain electrode 244 composed of
the same layer as the source electrode 243 via a contact hole 244a
extending through the gate insulating layer 282 and the first
interlayer insulating layer 283.
[0079] The top of the first interlayer insulating layer 283, on
which the source electrode 243 and the drain electrode 244 are
formed, is covered with a second interlayer insulating layer 284
mainly composed of, for example, an acrylic resin. This second
interlayer insulating layer 284 may also be composed of another
material, for example, a silicon compound such as SiN and
SiO.sub.2. If the second interlayer insulating layer 284 is
composed of such a silicon compound having a high gas barrier
property, particularly a compound of silicon and nitrogen, it can
inhibit the infiltration of oxygen, water, and so on through the
substrate 20 into the luminescent layers 60 to prolong the life of
the luminescent elements even if the substrate 20 is composed of a
moisture-permeable resin.
[0080] The pixel electrode 23, which is composed of ITO, is formed
on the second interlayer insulating layer 284. The pixel electrode
23 is connected to the drain electrode 244 via a contact hole 23a
provided in the second interlayer insulating layer 284. That is,
the pixel electrode 23 is connected to the heavily doped drain
region 241D of the silicon layer 241 via the drain electrode
244.
[0081] TFTs (drive circuit TFTs) included in the scanning-line
drive circuits 80 and the check circuit 90 (for example, p-channel
or n-channel TFTs in inverters included in the shift registers)
have the same structure as the above drive TFTs 123, though the
drive circuit TFTs are not connected to the pixel electrodes
23.
[0082] A bank composite of the pixel electrodes 23, a lyophilic
control layer 25, and organic bank layers 221 is provided on the
second interlayer insulating layer 284. The lyophilic control layer
25 is mainly composed of, for example, a lyophilic material such as
SiO.sub.2 while the organic bank layers 221 are composed of, for
example, an acrylic or polyimide resin. The
hole-injection/transport layers 70 and the luminescent layers 60,
in that order, are deposited on the pixel electrodes 23 in openings
25a provided in the lyophilic control layer 25 and bank openings
221a defined by the organic bank layers 221. In this embodiment,
the term "lyophilic" means that the control layer 25 is at least
more lyophilic than the material for the organic bank layers 221,
such as acrylic and polyimide resins.
[0083] The above-described layers up to the second interlayer
insulating layer 284 on the substrate 20 constitute the circuit
part 11.
[0084] Method for Manufacturing Organic EL Device
[0085] According to an embodiment of the present invention, an
example of methods for manufacturing the organic EL device 1 will
now be described with reference to FIGS. 6 to 9. The sectional
views in FIGS. 6 to 9 correspond to the sectional view taken along
line A-B in FIG. 2.
[0086] Referring to FIG. 6(a), the underlying protective layer 281
is formed on the substrate 20. An amorphous silicon layer 501 is
formed on the underlying protective layer 281 by, for example, ICVD
or plasma CVD, and crystal grains are then allowed to grow by laser
annealing or rapid heating to form a polysilicon layer.
[0087] Referring to FIG. 6(b), this polysilicon layer is patterned
by photolithography to form silicon layers 241, 251, and 261
isolated from each other. The silicon layers 241 are formed in the
effective display region 4 as components of the drive TFTs 123,
which are connected to the pixel electrodes 23. The silicon layers
251 and 261 are components of p-channel and n-channel TFTs (drive
circuit TFTs), respectively, included in the scanning-line drive
circuits 80.
[0088] The gate insulating layer 282, which is composed of a
silicon oxide film having a thickness of about 30 to 200 nm, is
formed on the entire surface of the silicon layers 241, 251, and
261 and the underlying protective layer 281 by, for example, plasma
CVD or thermal oxidation. If the gate insulating layer 282 is
formed by thermal oxidation, the silicon layers 241, 251, and 261
can be simultaneously crystallized into polysilicon layers.
[0089] If the silicon layers 241, 251, and 261 are subjected to
channel doping, boron ions, for example, are implanted into them at
a dosage of about 1.times.10.sup.12 cm.sup.2 at this time. As a
result, the silicon layers 241, 251, and 261 become lightly doped
p-type silicon layers having a doping concentration of about
1.times.10.sup.17 cm.sup.3 (determined after activation
annealing).
[0090] An ion-implantation-selection mask is formed above parts of
the silicon layers 241 and 261. Phosphorus ions are then implanted
at a dosage of about 1.times.10.sup.15 cm.sup.2. As a result, the
dopant is self-aligned to the mask to form the heavily doped source
region 241S and the heavily doped drain region 241D in each silicon
layer 241 and a heavily doped source region 261S and a heavily
doped drain region 261D in each silicon layer 261, as shown in FIG.
6(c).
[0091] Referring to FIG. 6(c), a conductive layer 502 for forming
gate electrodes is formed on the entire surface of the gate
insulating layer 282. This conductive layer 502 is composed of a
doped silicon film, a silicide film, or a metal film such as an
aluminum film, a chromium film, and a tantalum film, and has a
thickness of about 500 nm. The conductive layer 502 is patterned to
form gate electrodes 252 that are components of p-channel drive
circuit TFTs, the gate electrodes 242, which are components of
pixel TFTs, and gate electrodes 262 that are components of
n-channel drive circuit TFTs, as shown in FIG. 6(d). The drive
control signal conducting parts 320 (350) and first cathode power
wiring layers 121 are formed at the same time. The drive control
signal conducting parts 320 (350) are provided in the dummy region
5.
[0092] Referring to FIG. 6(d), phosphorus ions are implanted into
the silicon layers 241, 251, and 261 at a dosage of about
4.times.10.sup.13 cm.sup.2 using the gate electrodes 242, 252, and
262 as masks. As a result, the dopant is self-aligned to the gate
electrodes 242, 252, and 262 to form the lightly doped source
region 241b and the lightly doped drain region 241c in each silicon
layer 241, a lightly doped source region 261b and a lightly doped
drain region 261c in each silicon layer 261, and a lightly doped
regions 251S and 251D in each silicon layer 251.
[0093] Referring to FIG. 7(e), an ion-implantation-selection mask
503 is formed on the entire surface of the substrate 20 other than
parts for the p-channel drive circuit TFTs including the gate
electrodes 252. Using the mask 503, boron ions are implanted into
the silicon layers 251 at a dosage of about 1.5.times.10.sup.15
cm.sup.2. As a result, the dopant is self-aligned to the gate
electrodes 252, which function as masks, to counterdope the lightly
doped regions 251S and 251D into source and drain regions of the
p-channel drive circuit TFTs.
[0094] Referring to FIG. 7(f), the first interlayer insulating
layer 283 is formed on the entire surface of the substrate 20. This
first interlayer insulating layer 283 is then patterned by
photolithography to form contact holes C at positions at which the
source and drain electrodes of the TFTs are to be formed.
[0095] Referring to FIG. 7(g), the first interlayer insulating
layer 283 is covered with a conductive layer 504 that is composed
of a metal such as aluminum, chromium, and tantalum and has a
thickness of about 200 to 800 nm. Subsequently, patterning masks
505 are formed on regions 240a of the conductive layer 504 on which
the source and drain electrodes of the TFTs are to be formed,
regions 310a on which the drive voltage conducting parts 310 (340)
are to be formed, and regions 122a on which second cathode power
wiring layers are to be formed. Referring to FIG. 8(h), the
conductive layer 504 is patterned to form source electrodes 243,
253, and 263 and drain electrodes 244, 254, and 264.
[0096] Referring to FIG. 8(i), the first interlayer insulating
layer 283, on which the above components are formed, is covered
with the second interlayer insulating layer 284, which is composed
of, for example, a polymeric material such as an acrylic resin and
preferably has a thickness of about 1 to 2 .mu.m. The second
interlayer insulating layer 284 may also be composed of SiN or
SiO.sub.2. If the second interlayer insulating layer 284 is
composed of SiN, it preferably has a thickness of 200 nm. If, on
the other hand, the second interlayer insulating layer 284 is
composed of SiO.sub.2, it preferably has a thickness of 800 nm.
[0097] Referring to FIG. 8(j), the second interlayer insulating
layer 284 is etched to remove the parts corresponding to the drain
electrodes 244 of the drive TFTs 123, thus forming the contact
holes 23a.
[0098] Referring to FIG. 9(k), a transparent conductive film for
forming the pixel electrodes 23 is formed on the entire surface of
the substrate 20 and is patterned to provide the pixel electrodes
23 in the effective display region 4 and dummy electrodes 26 in the
dummy region 5. The pixel electrodes 23 are connected to the drain
electrodes 244 via the contact holes 23a in the second interlayer
insulating layer 284. In FIGS. 3 and 4, the pixel electrodes 23 and
the dummy electrodes 26 are collectively referred to as the pixel
electrodes 23.
[0099] The dummy electrodes 26 are not connected to the lower metal
wiring through the second interlayer insulating layer 284. These
dummy electrodes 26, which are isolated from each other and have
substantially the same shape as the pixel electrodes 23 in this
embodiment, may have a different configuration from the pixel
electrodes 23. In this case, the dummy electrodes 26 at least
include those disposed above the drive voltage conducting parts 310
(340).
[0100] Referring to FIG. 9(l), the lyophilic control layer 25,
which is an insulating layer, is formed on the pixel electrodes 23,
the dummy electrodes 26, and the second interlayer insulating layer
284. This lyophilic control layer 25 has an opening 25a (see also
FIG. 3) on each pixel electrode 23 to allow the transfer of holes
from the pixel electrode 23. On the other hand, the lyophilic
control layer 25 has no opening on each dummy electrode 26, thus
blocking the transfer of holes at the dummy electrode 26.
[0101] The lyophilic control layer 25 also has depressions formed
between every two adjacent pixel electrodes 23. A BM is formed on
the depressions of the lyophilic control layer 25. Specifically,
metal chromium is deposited on the depressions by sputtering.
[0102] Referring to FIG. 9(m), the organic bank layers 221 are
formed on predetermined positions of the lyophilic control layer
25, namely, on the BM. Specifically, for example, an organic layer
for forming the organic bank layers 221 is formed by coating, such
as spin coating and dip coating, with a solution of a resist such
as acrylic and polyimide resins. This organic layer may be composed
of any material that is insoluble to an ink solvent described later
and that is readily patterned by, for example, etching.
[0103] The organic layer is then etched by, for example,
photolithography to form the bank openings 221a, thus providing the
organic bank layers 221. The organic bank layers 221 have wall
surfaces in the bank openings 221a. In this case, the organic bank
layers 221 at least include those disposed above the drive control
signal conducting parts 320.
[0104] Subsequently, lyophilic regions and liquid-repellent regions
are provided on the surfaces of the organic bank layers 221. In
this embodiment, these regions are provided through a plasma
processing step. Specifically, this plasma processing step includes
the substeps of preheating the substrate 20; subjecting the top and
wall surfaces of the organic bank layers 221, electrode surfaces
23c of the pixel electrodes 23, and the top surface of the
lyophilic control layer 25 to lyophilic treatment; subjecting the
top and wall surfaces of the organic bank layers 221 to
liquid-repellent treatment; and cooling the substrate 20.
[0105] That is, the overall substrate 20 is heated to a
predetermined temperature, for example about 70.degree. C. to
80.degree. C., is subjected to plasma processing using oxygen as a
reactive gas (O.sub.2 plasma processing) in air at the substep of
the lyophilic treatment, is subjected to plasma processing using
tetrafluoromethane as a reactive gas (CF.sub.4 plasma processing)
in air at the substep of the liquid-repellent treatment, and is
cooled to room temperature. This plasma processing step provides
the lyophilic and liquid-repellent regions at predetermined
positions.
[0106] The CF.sub.4 plasma processing, though slightly affecting
the electrode surfaces 23c of the pixel electrodes 23 and the
lyophilic control layer 25, maintains their lyophilicity. Hydroxyl
groups provided at the substep of the lyophilic treatment are not
replaced by fluorine radicals because ITO, which is an example of
the material for the pixel electrodes 23, and SiO.sub.2 and
TiO.sub.2, which are examples of the material for the lyophilic
control layer 25, lack an affinity for fluorine.
[0107] Referring to FIG. 10(n), a step of forming the
hole-injection/transport layers 70 is performed. This step is
preferably performed by droplet discharging, particularly
inkjetting. The hole-injection/transport layers 70 are formed on
the pixel electrodes 23 by selectively applying, drying, and
heat-treating the material for the hole-injection/transport layers
70 on the electrode surface 23c of the pixel electrodes 23. An
example of the material for the hole-injection/transport layers 70
is a solution of PEDOT/PSS, which has been described above, and a
polar solvent such as isopropyl alcohol.
[0108] First, the material for the hole-injection/transport layers
70 is charged into an inkjet heat (not shown in the drawings). A
discharging nozzle of the inkjet head is opposed to the electrodes
surfaces 23c in the openings 25a provided in the lyophilic control
layer 25. A predetermined amount of droplet is applied from the
discharging nozzle onto each electrode surface 23c while the inkjet
head and the overall substrate 20 are relatively shifted. The
applied droplets are dried to evaporate the dispersion medium or
solvent contained, thus forming the hole-injection/transport layers
70.
[0109] The droplets applied from the discharging nozzle cover the
electrode surfaces 23c and accumulate in the openings 25a of the
lyophilic control layer 25 because the electrode surfaces 23c have
been subjected to lyophilic treatment. On the other hand, the
droplets are repelled by the top surfaces of the organic bank
layers 221 because the top surfaces of the organic bank layers 221
have been subjected to liquid-repellent treatment. The droplets
thus fail to adhere to the top surfaces of the organic bank layers
221. Hence, even if the droplets deviate from predetermined
discharging positions and part of the droplets is applied on the
surfaces of the organic bank layers 221, the droplets do not wet
the surfaces of the organic bank layers 221 and are repelled and
drawn into the openings 25a of the lyophilic control layer 25.
[0110] The steps following the step of forming the
hole-injection/transpor- t layers 70 are preferably performed in an
atmosphere of an inert gas such as nitrogen and argon to inhibit
the oxidation and moisture adsorption of the constituent materials
used and the components formed.
[0111] A step of forming the luminescent layers 60 is then
performed. This step is preferably performed by inkjetting, which
is a droplet discharging method, as in the step of forming the
hole-injection/transpor- t layers 70. A material for forming the
luminescent layers 60 is applied, dried, and heat-treated on the
hole-injection/transport layers 70 to form the luminescent layers
60 in the bank openings 221a defined by the organic bank layers
221, namely, in pixel areas. In the step of forming the luminescent
layers 60, a nonpolar solvent that is insoluble to the
hole-injection/transport layers 70 is used as the ink solvent for
forming the luminescent layers 60 to inhibit the redissolution of
the hole-injection/transport layers 70. The formation of the
luminescent layers 60 is performed for each color.
[0112] A step of forming the electron-injection layer 52 on the
luminescent layers 60 is then performed. An organic metal complex
having a central atom of the same element as a constituent element
(for example, Ca) of the cathode 50 is used for the
electron-injection layer 52. This electron-injection layer 52 may
be formed by a known method such as resistance heating deposition
and coating. For example, the above complex (for example,
Ca(acac).sub.2) is dissolved in a solvent, is applied on the entire
surface of the substrate 20 by spin coating, and is dried to form
the electron-injection layer 52.
[0113] In the step of forming the electron-injection layer 52, the
above complex may be formed by deposition. In this case, for
example, an organic material (for example, acac) for forming a
ligand of the complex is deposited on the entire surface of the
substrate 20 so as to cover exposed parts of the luminescent layers
60, and a constituent metal (for example, Ca) of the cathode 50 is
deposited on the organic material. The deposited metal atoms
combine with the previously deposited ligand molecules to form the
electron-injection layer 52. This deposition is continued to form
part of the cathode 50 (in the vicinity of the interface to the
electron-injection layer 52). Subsequently, for example, Al or ITO
is further deposited on the part of the cathode 50 to form the
cathode 50, which is composed of a laminate of the Ca film and the
Al or ITO film. According to this method, the single deposition
step enables successive formation of the electron-injection layer
52 and part of the cathode 50, thus facilitating the process.
[0114] If an organic metal complex having a central atom and
chelating and neutral ligands surrounding the central atom is used
for the electron-injection layer 52, the electron-injection layer
52 may be formed by a known method such as resistance heating
deposition and coating. Examples (a) to (e) of the method used will
now be described.
[0115] (a) Method for Co-Depositing Neutral Ligand and Complex
[0116] In this method, a metal element having a low work function
is selected for the central atom and is co-deposited with organic
materials for the chelating and neutral ligands on the entire
surface of the substrate 20. Alternatively, an organic metal
complex (first organic metal complex) having the same number of
chelating ligands as the valence of the above central atom is
co-deposited with the organic material for the neutral ligand to
form an organic metal complex (second organic metal complex) having
a larger number of ligands than the valence of the central
atom.
[0117] The co-deposition enables cathode design suited to the
luminescent material used because known complex and ligand
materials can be freely combined in a deposition machine. In
addition, an organic metal complex having any composition can be
provided by changing deposition conditions (for example, the
deposition temperature of the complex and the ligands), so that the
element structure can be readily optimized. The complex preferably
has a central atom of the same element as a constituent element of
the cathode 50, which is formed in a subsequent step. Such a
complex can adhere more strongly to the cathode 50. Furthermore,
this element, even if diffusing downward during the formation of
the cathode 50, does not act as an impurity on the
electron-injection layer 52, thus contributing to the electrical
stability of the elements.
[0118] (b) Method for Co-Depositing Neutral Ligand and Different
Types of Complexes
[0119] In this method, optimum organic metal complexes (first
organic metal complexes) selected for the individual types of the
R, G, and B luminescent layers 60 are co-deposited with the organic
material for the neutral ligand on the entire surface of the
substrate 20 to form organic metal complexes (second organic metal
complexes) having a larger number of ligands than the valence of
the central atom.
[0120] When each pixel includes R, G, and B luminescent layers as
in this embodiment, the different types of luminescent layers may
have different optimum complexes. If only a single complex is
formed on the luminescent layers as in method (a), the complex
cannot necessarily have a desirable effect on all types of
luminescent layers. According to this method, on the other hand,
the electron-injection layer 52 formed contains a mixture of
different complexes corresponding to the individual types of the
luminescent layers 60, thus having an excellent electron-injection
effect on all types of the luminescent layers 60. According to this
method, additionally, the color balance can be adjusted by changing
the deposition conditions (for example, deposition temperature) of
the complexes.
[0121] (c) Method for Coating Entire Surface of Substrate with
Complexes
[0122] In this method, optimum organic metal complexes (first
organic metal complexes) selected for the individual types of the
R, G, and B luminescent layers 60 are dissolved in a solvent to
prepare a common coating solution. This coating solution is applied
on the entire surface of the substrate 20 by, for example, spin
coating. This coating is dried to form complexes having the same
number of chelating ligands as the valence of the central atom on
the luminescent layers 60 (a substep of forming the first organic
metal complexes). A polar solvent that is insoluble to the
luminescent layers 60 is used as the solvent for the coating
solution to inhibit the redissolution of the luminescent layers 60.
The organic material for the neutral ligand is then deposited on
the complexes to coordinate the neutral ligand to the central atom
(a substep of forming the second organic metal complexes).
[0123] This method is the same as method (b) except that a wet
process (namely, coating) is employed; therefore, this method
provides the same structure as method (b). In this method, a
coating solution of organic metal complexes to which the neutral
ligand has been coordinated may be applied. As the number of the
ligands coordinated is increased, the polarities of the complexes
are lowered and accordingly a solvent having a lower polarity is
required for preparing the coating solution. A coating solution
prepared using such a solvent having a lower polarity may
redissolve the luminescent layers 60. To avoid such an accident,
preferably, complexes having no neutral ligand (namely, complexes
having less ligands) are used in the coating step, and the step of
coordinating the neutral ligand is performed separately from the
coating step.
[0124] (d) Method for Separately Forming Electron-Injection Layer
on Each Luminescent Layer
[0125] In this method, optimum organic metal complexes (first
organic metal complexes) selected for the individual types of the
R, G, and B luminescent layers 60 are used to prepare coating
solutions for the individual types of the luminescent layers 60.
Each coating solution is selectively applied onto the corresponding
type of the luminescent layers 60 by droplet discharging (for
example, inkjetting). These coatings are dried to form separate
electron-injection layers on the individual luminescent layers 60
(the substep of forming the first organic metal complexes). The
organic material for the neutral ligand is then deposited on the
complex to coordinate the neutral ligand to the central atom (the
substep of forming the second organic metal complexes).
[0126] According to methods (a) to (c), the electron-injection
layer 52 is homogeneously formed on substantially the entire
surface of the substrate 20 in contrast to the steps of forming the
hole-injection/transport layers 70 and the luminescent layers 60,
where the materials used are selectively applied only onto the
pixel areas. This electron-injection layer 52, though simplifying
the manufacture, cannot necessarily have a desirable
electron-injection effect on all types of the luminescent layers
60. In this method, on the other hand, optimum coating solutions
adjusted for the individual types of the luminescent layers 60 are
selectively applied onto the corresponding types of the luminescent
layers 60 by droplet discharging to form the complexes. This method
therefore enables separate material design for the individual types
of the luminescent layers 60, thus maximizing the luminescent
efficiency of each type of the luminescent layers 60 and
facilitating the adjustment of color balance.
[0127] (e) Method for Applying Complexes Together with Organic
Material for Neutral Ligand
[0128] In this method, optimum organic metal complexes (first
organic metal complexes) selected for the individual types of the
R, G, and B luminescent layers 60 are mixed with the organic
material for the neutral ligand in a solvent to prepare coating
solutions for the individual types of the luminescent layers 60.
These coating solutions are selectively applied onto the
corresponding types of the luminescent layers 60 by droplet
discharging. These coatings are dried to form separate
electron-injection layers on the individual luminescent layers
60.
[0129] This method is the same as method (d) except that the
neutral ligand is formed by a wet process; therefore, this method
provides the same structure as method (d). According to this
method, the electron-injection layers are formed by a wet process,
so that the overall process for manufacturing the luminescent
elements, including the above steps of forming the
hole-injection/transport layers 70 and the luminescent layers 60,
can be performed by a wet process.
[0130] Referring to FIG. 10(o), a step of forming the cathode 50 is
performed by deposition. In this step, a film of a metal (for
example, Ca) having a low work function is formed on the entire
exposed part of the electron-injection layer 52 by deposition or
sputtering, and a film of another metal (for example, Al or ITO)
having a higher work function than the above metal is formed on the
metal film. As a result, the cathode 50 is formed, which is
composed of a laminate of the Ca and Al (or ITO) films.
Alternatively, in this step, Al (or ITO) may be directly deposited
on the electron-injection layer 52 to form the cathode 50, which is
composed of an Al (or ITO) monolayer film. In this case, an organic
metal complex having a central atom of Al, which is a constituent
material of the cathode 50, may be used for the electron-injection
layer 52 to enhance the adhesion between the cathode 50 and the
electron-injection layer 52.
[0131] Finally, a sealing step of forming the sealing substrate 30
is performed. In this sealing step, the substrate 20 and the
sealing substrate 30 are sealed with the sealing resin 40 while a
desiccant 45 is inserted between them. This sealing step is
preferably performed in an atmosphere of an inert gas such as
nitrogen, argon, and helium.
[0132] According to this embodiment, as described above, an organic
metal complex is used for the electron-injection layer 52 to
enhance the adhesion of the electron-injection layer 52 to the
cathode 50, which is composed of a metal, and to the luminescent
layers 60, which are composed of an organic material. This
embodiment can therefore improve the luminescent efficiency of each
type of the R, G, and B luminescent layers 60.
[0133] In particular, this embodiment, in which a larger number of
ligands than the valence of the central atom of the organic metal
complex are coordinated to the central atom, can inhibit the
deterioration of the electron-injection layer 52 during, for
example, the formation of the cathode 50 more reliably than known
methods.
[0134] The known organic metal complex described above has a
central atom to which chelating ligands are coordinated. The number
of the ligands corresponds to the valence of the central atom. If
the central atom is of an element having a smaller valence number
(for example, an alkali metal), fewer ligands surround the central
atom (for example, the above known complex has one ligand).
Consequently, as described above, the central atom may be separated
from the ligands, depending on the deposition conditions of the
cathode 50. In general, the coordination number of the central atom
is larger than the valence of the central atom. If ligands other
than the chelating ligands (for example, neutral ligands such as
heterocyclic amines) are coordinated to the central atom as in this
embodiment, the central atom can have a larger number of ligands
than the valence of the central atom. The coordination bond of
ligands other than the chelating ligands to the central atom can
increase the chemical stability of the complex. In addition, these
ligands surround the central atom to act as steric hindrance,
thereby stably holding the central atom. This embodiment can
therefore increase the stability of the complex to inhibit the
intrusion of impurities into the luminescent layers 60, thus
providing an organic EL device having high luminescent efficiency
and stable characteristics. Furthermore, higher complex stability
leads to higher moisture resistance.
EXAMPLES
[0135] Examples of the present invention will now be described.
[0136] In an example of the present invention, R, G, and B
luminescent elements were prepared using the above materials. The
specific process of this example is described below. First, ITO was
deposited on a glass substrate to form anodes. PEDOT was then
applied onto the anodes and was dried to form
hole-injection/transport layers. Luminescent materials having a
n-conjugated fluorene skeleton, as described above, were applied
onto the hole-injection/transport layers and were dried to form
organic luminescent layers. These luminescent layers were coated
with Ca(acac).sub.2, which is a .beta.-diketone complex. This
coating was dried to form an electron-injection layer having a
thickness of 0.5 nm on the luminescent layers. Finally, a Ca film
having a thickness of 20 nm and an Al film having a thickness of
200 nm were deposited to form a cathode, thus providing a
bottom-emission EL device.
[0137] On the other hand, as a comparative example, an EL device
was produced which has the same structure as that in the above
example, except that the electron-injection layer was composed of
LiF.
[0138] Tables 1 and 2 show the initial characteristics of the
devices (luminous intensity (cd/m.sup.2) during the application of
a voltage of 6 V; and luminescent efficiency (cd/A)). In Table 1,
the luminous intensity and luminescent efficiency of the device in
the example of the present invention are normalized with reference
to the data of the device in the comparative example.
1TABLE 1 Luminous intensity (cd/m.sup.2) Comparative at 6 V example
Example (normalized) LiF/Ca/Al Ca(acac).sub.2/Ca/Al Red 1 2.23
Green 1 2.56 Blue 1 1.25
[0139]
2TABLE 2 Comparative Efficiency (cd/A) example Example (normalized)
LiF/Ca/Al Ca(acac).sub.2/Ca/Al Red 1 1.16 Green 1 1.24 Blue 1
1.29
[0140] Tables 1 and 2 indicate that the R, G, and B luminescent
elements in the example of the present invention have higher
luminous intensity and luminescent efficiency than those in the
comparative example.
[0141] In the example of the present invention, another EL device
including a different cathode was produced. This cathode was
composed of an Al monolayer film having a thickness of 200 nm, and
accordingly the electron-injection layer of this device was
composed of an Al(acac).sub.2 film having a thickness of 0.5 nm. A
still another EL device was produced which was a top-emission
device including a cathode composed of a laminate of a Ca film
having a thickness of 5 nm and an ITO film having a thickness of 50
nm and an electron-injection layer composed of a Ca(acac).sub.2
film having a thickness of 0.5 nm. The R, G, and B luminescent
elements of these devices were found to have higher luminous
intensity and luminescent efficiency than those in the comparative
example.
[0142] Electronic Appliance
[0143] Electronic appliances including an organic EL device
according to the present invention will now be described. An
example of electronic appliances of the present invention includes
the organic EL device described above as a display, and is shown in
FIG. 11.
[0144] FIG. 11 is a perspective view of an example of cellular
phones. In FIG. 11, a cellular phone 1000 has a display composed of
an organic EL device 1001 according to the present invention. This
cellular phone 1000, including the organic EL device 1001, provides
a long life and a bright display.
[0145] The present invention is not limited to the above
embodiments, and various modifications are permitted within the
scope of the present invention.
[0146] For example, the luminescent layers 60, which are composed
of a polymeric material in the above embodiment, may be composed of
a low-molecular-weight material. In addition, the above circuit
part 11, which is an example, may have a different structure.
Furthermore, the organic EL device of the present invention, which
is applied to a display in the above embodiment, may be used as a
backlight (lighting device) for, for example, transmissive liquid
crystal displays by forming the luminescent layers 60 on the entire
surface of the substrate 20.
* * * * *